Diamond coated body and method of its production

ABSTRACT

There is now provided a body coated with at least one diamond layer on a substrate of cemented carbide or cermets. The substrate is before the diamond coating process provided with spotwise occurring particles containing an element either being any of W, Ta, Ti, Mo Cr, V, Nb, Mg, Ca, Na, K or, preferably, any of B, Si, S, Al or P. These particles are dispersed at a density giving an average distance between two particles of 20 μm or less, preferably 5 μm or less.

BACKGROUND OF THE INVENTION

The present invention relates to a diamond coated body with goodadherence of the diamond layer and a high resistance to wear. Inparticular, the presently claimed invention relates to a cutting toolfor cutting Al-alloys containing, e.g., Si and Cu as alloying elementsand the like.

The production of thin layers of diamond directly from the gas phase byCVD or PVD technique is of great interest for the coating of cuttingtools, drill bits, knives, etc. Gas phase deposition of diamond atuseful deposition rates has been the subject for numerous researchersand a number of methods have evolved, all of which are plasma CVDmethods.

The commercialization of diamond coated cutting tools has involvedseveral years of research efforts, where the main problem has beenachieving sufficient diamond layer adhesion onto the tool substratematerial in a large-scale production method in order to make diamondcoated cutting tools competitive from an economical point of view. Atthis stage, these problems have been generally solved and diamond coatedcutting tools are produced and sold, see, I. Reineck, M. E. Sjostrand,J. Kamer, M. Pedrazzini, "HCDCA Diamond-Coated Cutting Tools", Diamondand Related Materials 5, 1996, pages 819-824. Having reached this levelof development, further focus on production cost related issues is ofvital importance.

The substrates of interest for diamond layers in cutting applicationsinclude cemented carbides and ceramics such as SiAlON and Si₃ N₄ and thedeposition of diamond on these categories of substrates is well-known inthe art. A standard method for achieving good diamond adhesion oncemented carbide substrates is to use diamond particles suspended in anultrasonic bath wherein the tools substrates to be coated are treatedprior to diamond deposition in order to scratch the tool surfaces toenhance the nucleation density. A high nucleation density is, however,not sufficient for achieving a good diamond layer adhesion--otherparameters, such as control of the binder phase activity, in particular,that of cobalt, in a surface region is also important. Much work hasbeen devoted to the enhancement of nucleation density for diamondgrowth, see, e.g., page 1173 of H. Liu and D. S. Dandy, "Studies onNucleation Process in Diamond CVD: An Overview of Receipt Developments",Diamond and Related Materials 4, 1995, pages 1173-1188, for a review.

In B. Lux and R. Haubner, "Nucleation and Growth of Low-PressingDiamond", Diamond and Diamond-like Films and Coatings, ed. R. E.Clausing et al., 1991, Plenum Press, New York, pages 579-609, polishingwith Al₂ O₃ (1 μm) is said not to enhance the nucleation density whilethis effect is obtained with diamond grits.

In U.S. Pat. No. 5,164,051, electrolytic polishing of cemented carbide,optionally combined with subsequent scratching with diamond, cBN, Al₂ O₃or SiC is described. Diamond is the preferred scratching agent. Theindication for good diamond layer adhesion is measured by means of aRockwell indentation test where the layers are said to withstand a loadof 5-25 kg without flaking.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of this invention to avoid or alleviate the problems ofthe prior art.

It is further an object of this invention to provide a diamond coatedbody where the diamond layer adheres well and has a high resistance towear.

In one aspect of the invention there is provided a body of cementedcarbide or cermets coated with at least one diamond layer in whichbetween said body and diamond layer are particles containing at leastone element taken from the group consisting of W, Ta, Ti, Mo, Cr, V, Nb,Mg, Ca, Na, K, B, Si, S, Al, P and mixtures thereof, said particlesbeing dispersed at an average distance between two particles of 10 μm orless.

In another aspect of the invention there is provided a method forproducing a diamond coated body comprising treating the body to obtain asuitable surface region depleted of cobalt, treating the bodies in anultrasonic bath containing particles containing at least one elementtaken from the group consisting of W, Ta, Ti, Mo, Cr, V, Nb, Al, Mg, Ca,Na, K, B, Si, S, P and mixtures thereof in a concentration of 2-50 g/lfor about 30-60 minutes to produce a body having particles of an averagesize of either less than 5 μm, or between 7-20 μm on the surface andthen coating said bodies with diamond by plasma-CVD technique.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an analysis obtained by electron probe microanalyzer of thesurface of a body of the present invention after pretreatment.

FIG. 2 is an analysis obtained by electron probe microanalyzer of thesurface of a body which has been conventionally prepared withoutpretreatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

It is surprising to find that the flaking resistance as well as the wearresistance of a diamond layer deposited on a cemented carbide or ceramicbody, in particular, a cutting tool insert, can be obtained to a levelat least as good as for diamond layers deposited onto tool bodiesprepared by ultrasonic pretreatment with diamond particles. This isachieved through a combination of ultrasonic pretreatment with particlesconsisting of, e.g., B₄ C, Al₂ O₃ or SiC, and the removal of bindermaterial, e.g., cobalt, in a surface region of the tool substrate. Inaddition, the substrate surface should be prepared as to have either acertain surface roughness or to have pores in a surface region. Usingparticles other than diamond for the predeposition preparation isfavorable from the view of production costs.

According to the presently claimed invention, the particles provided bythe pretreatment can be stuck onto the substrate surface as can be seenby analyzing the surface in an electron probe microanalyzer, see,FIG. 1. The distribution of Al-enriched particles should be compared tothat of a substrate surface that is not treated according to thepresently claimed invention as shown in FIG. 2.

According to the presently claimed invention, there is now provided abody coated with at least one diamond layer. The surface of the bodybeing in contact with the diamond layer is enriched with particlescontaining at least 20 weight % of B, Al and/or Si, such as carbides,oxides or nitrides of these, e.g., B₄ C, BN, SiC or Al₂ O₃, preferablyAl-containing particles. Particles containing S and/or P can also beused as well as metal-containing particles where the metal is at leastone of W, Cr, Mo, Ta, Ti, Nb, V, Mg, Ca, Na or K.

The average size of the particles is less than 5 μm, preferably lessthan 2 μm, and most preferably less than 0.5 μm. Alternatively, theaverage size of the particles is 7-20 μm, preferably 10-15 μm. Inanother alternative, a combination of small, <0.5 μm, and largeparticles, 10-15 μm, is present, using at least 25% of each kind.

The particle distribution is such that the average distance x_(m)between two particles as analyzed by electron microprobe analysis isless than 10 μm, preferably less than 5 μm, where x_(m) =Σx_(i) /n wherex_(i) are the individual distances between the nearest neighbors ofparticles as shown in FIG. 1 and n is the number of such pairs, n being>5.

The surface roughness of the body before the particles are attached is1<R_(a) <20 μm, preferably 1<R_(a) <10 μm. In an alternative embodiment,with a surface roughness of R_(a) <1 μm, there are provided pores in asurface region of depth <10 μm, preferably <5 μm. The size of the poresis 0.5-5 μm, preferably 0.5-2 μm.

The bodies according to the presently claimed invention include cementedcarbides and cermets. Preferably, a cemented carbide body is depleted inthe surface zone with respect to cobalt. This can, for example, be doneby partly carburizing an eta phase-containing body as disclosed in U.S.Ser. No. 08/214,157 (our reference: 024000-807).

According to the presently claimed invention, there is also provided amethod of preparing bodies suited for coating with diamond layersshowing good adhesion. The bodies are first treated in order to get asurface roughening or creation of pores and depletion of cobalt, eitherthrough a sintering process which roughens the surface, or by etchingthe binder material to create pores in the surface region. Such methodsare well-known in the art. Subsequently, the bodies are treated in anultrasonic bath containing the above-mentioned particles in aconcentration of 2-50 g/l in water, oil or other suitable liquid forabout 30-60 minutes. The average size of The particles used (andtherefore deposited on the surface) is less than 5 μm, preferably lessthan 2 μm, and most preferably less than 0.5 μm. As an alternativemethod of treatment, particles of average size, 7-20 μm, preferably10-15 μm, are used. In a preferred method, the bodies are treated usingparticles of average size, 10-15 μm, and of average size, less than 0.5μm, either simultaneously in one treatment, using at least 25% of eachkind, or separately in two consecutive treatments.

As an alternative method of providing the particles to the surfaces ofthe substrates, a solution containing the desired elements can be usedout of which particles are precipitated.

After the body is treated to provide the particle-containing surface, adiamond layer is applied by conventional plasma-CVD techniques known tothe skilled artisan.

The presently claimed invention has been described with reference to adiamond layer in direct contact with a cemented carbide or cermet body.It is obvious that the invention can be applied also to the case whenone or more intermediate layers are present between the body and thediamond layer.

The presently claimed invention can be applied to diamond coated cuttingtools, tools for rock drilling and wear parts as well as to othersuperhard layerss, such as cBN layers deposited by CVD or PVD methods.

The invention is additionally illustrated in connection with thefollowing Examples which are to be considered as illustrative of thepresent invention. It should be understood, however, that the inventionis not limited to the specific details of the Examples.

EXAMPLE 1

Six WC-6% Co cemented carbide inserts with a cobalt depleted surfacezone and a surface roughness of R_(a) =2.0 μm were first treated in anultrasonic bath containing 1 g B₄ C-powder of a grain size of 5-15 μm in200 ml of oil as a suspending medium. The treatment time was 30 minutes.The inserts were subsequently ultrasonically treated in a suspensionconsisting of Al₂ O₃ powder of a grain size of <0.5 μm at aconcentration of 1 g per 200 ml of oil for another 30 minutes. Theinserts were then cleaned in alcohol for 30 minutes in the ultrasonicbath.

The Al₂ O₃ -B₄ C pretreated inserts were analyzed in an electronmicroprobe with respect to Al. Particles containing Al were found toexist at an average distance of 4 μm between each two particles.

A set of reference WC-6% Co inserts were ultrasonically pretreated indiamond grit powder of a grain size of 0-2 μm suspended in oil. Thetreatment time, as well as the cleaning procedure, was the same as forthe above-mentioned inserts.

Subsequently, both types of inserts were diamond coated to a layerthickness of 7 μm using microwave plasma assisted CVD. The grain size ofthe layer was about 5 μm.

The inserts were subjected to a turning flaking test in an Al18% Cualloy using the following cutting data:

v=300 m/min

f=0.1 mm

a=1 mm

wet cutting

The diamond coated set of inserts pretreated according to the inventionlasted 6 minutes in this test, until a wear zone of a width of 0.1 mmwas formed, compared to the result for the set of insert pretreated withdiamond grit suspension which lasts only 4 minutes. Apart from theimprovement in tool life, the benefit of using a cheaper pretreatmentagent compared to the diamond grit is demonstrated.

EXAMPLE 2

Six WC-4% Co inserts with a cobalt depleted surface zone and a poroussurface layer of 5 μm with a pore size of 1 μm, were pretreated in anultrasonic suspension containing B₄ C powder of a grain sizedistribution of 0-5 μm. The treatment time was 30 minutes. The insertswere then ultrasonically cleaned in alcohol for 30 minutes. A set ofreference inserts was prepared in accordance with the reference insertsof Example 1. The inserts were coated with a 10 μm thick diamond layerusing a DC arc plasma CVD method.

Prior to diamond coating, the B₄ C treated inserts were analyzed in anelectron microprobe with respect to boron. Boron-containing particleswere found with an average distance of 4 μm between each two individualparticles.

The inserts were subjected to a milling flaking test in an Al-9% Sialloy using the following cutting data:

v=2000 m/min

f=0.5 mm/tooth

a=1 mm

wet cutting

The diamond coated set of inserts pretreated according to the presentlyclaimed invention lasted 100 passes in this test without any visibledamage. This result was also achieved for the diamond grit treated setof inserts. Hence, a similar performance can be achieved by using a B₄ Ctreatment instead of the more expensive diamond grit treatment.

EXAMPLE 3

Six WC-4% Co inserts with a cobalt depleted surface zone and a surfaceroughness of R_(a) =5 μm were treated in an ultrasonic bath containing 1g B₄ C of a grit size of 10 μm in 200 ml of oil for 30 minutes. Theinserts were subsequently treated in an aqueous Al₂ (SO₄)₃ solution(10%) for 5 minutes. An alkaline solution of 2% NaOH was then added tothe Al₂ (SO₄)₃ solution, still being stirred in the ultrasonic bath. Theinserts were treated in this bath for another 25 minutes. Then theinserts were ultrasonically cleaned in alcohol for 15 minutes. Referenceinserts were prepared in accordance with the reference inserts ofExample 1. All inserts were diamond coated in a DC plasma activated CVDprocess to a diamond layer thickness of 10 μm.

Prior to diamond coating the Al₂ (SO₄)₃ -treated inserts were analyzedin an electron microprobe with respect to aluminum. Aluminum-containingparticles were found at an average distance of 5 μm between each twoindividual particles.

The inserts were subjected to a turning flaking test in an Al 18% Cualloy using the following cutting data:

v=700 m/min

f=0.05 mm

a=-1 mm

wet cutting

The diamond coated set of inserts pretreated according to the presentlyclaimed invention lasted 4 minutes in this test compared to the resultfor the set of inserts pretreated with diamond grit suspension, whichwas 2 minutes. Again, an improvement in tool life is demonstrated,together with the benefit of using a cheaper pretreatment agent comparedto the diamond grit powder.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

What is claimed is:
 1. A body of cemented carbide or cermets coated withat least one diamond layer in which between said body and diamond layerare particles containing at least one element taken from the groupconsisting of B, Si, S, Al, P and mixtures thereof, said particles beingdispersed at an average distance between two particles of 10 μm or lessthe particles being a combination of small particles less than 0.5 μmand large particles of 10-15 μm with at least 25% of each of the smalland large particles being present.
 2. The body of claim 1 wherein theaverage distance between two particles is 5 μm or less.
 3. The body ofclaim 1 wherein said body is a cemented carbide with a cobalt depletedsurface zone.
 4. The body of claim 1 wherein said body has a surfaceroughness of 1 μm<R_(a) <20 μm.
 5. The body of claim 4 wherein said thesurface roughness is 1 μm<R_(a) <10 μm.
 6. The body of claim 1 whereinsaid body has a porous surface zone of <10 μm.
 7. The body of claim 6wherein the porous surface zone is <5 μm.